**1. Introduction**

The food packaging material in the form of polymeric edible films is gaining more attention these days due to its numerous benefits, such as being edible, biodegradable, nontoxic, biocompatible, etc. These films are made at a laboratory scale to improve the

**Citation:** Bhatia, S.; Al-Harrasi, A.; Alhadhrami, A.S.; Shah, Y.A.; Kotta, S.; Iqbal, J.; Anwer, M.K.; Nair, A.K.; Koca, E.; Aydemir, L.Y. Physical, Chemical, Barrier, and Antioxidant Properties of Pectin/Collagen Hydrogel-Based Films Enriched with *Melissa officinalis*. *Gels* **2023**, *9*, 511. https://doi.org/10.3390/ gels9070511

Academic Editors: Aris Giannakas, Constantinos Salmas and Charalampos Proestos

Received: 16 May 2023 Revised: 14 June 2023 Accepted: 15 June 2023 Published: 25 June 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

safety, quality, and shelf life of food products [1]. There are several manufacturers (Innoteq, NewGem Foods, Watson, Biofilm Limited, ODF Pharma, Proinec, MonoSol, Umang Pharmatech, etc.) that make edible films at large scale. Pectin, a major constituent of plant cells, is primarily used in the manufacturing of fruit juices, jams, and bread fillings [2,3]. The utilization of pectin as a polymer to produce hydrogel-based films is a viable option owing to its gelation characteristics, lack of toxicity, biodegradability, and accessibility. Collagen is one of the natural polymers that hold significant potential as a vital industrial raw material [4]. Its physicochemical characteristics, biodegradability, and non-toxicity have made it increasingly important and useful in the food sector [5].

Several research studies have shown that incorporating various plant-based bioactive components into pectin-based films can result in to effective food packaging material [6,7]. Blending two polymers (pectin/collagen) is an effective way to synthesize the edible film with favorable barrier and mechanical attributes. Hydrogel-based films have been formulated with essential oils due to their possible antibacterial, antioxidant, and antifungal characteristics [8]. Essential oils are widely used in the food industries due to their composition of volatile compounds, including a combination of terpenes, terpenoids, alpha-aromatic and aromatic compounds, as well as non-volatile compounds [9].

*Melissa officinalis* is a member of the Lamiaceae family and possesses diverse therapeutic properties, and Melissa oil exhibits antibacterial, antifungal, and antioxidant properties [10,11]. Melissa essential oil (MOEO) primarily comprises citronella, but it also contains other components such as citral, geraniol, linalool, and beta-caryophyllene [12]. In earlier research, researchers developed active films using a combination of carboxymethyl chitosan and locust bean gum. These films contained nanoemulsions of essential oil extracted from *Melissa officinalis* L. Following the analysis of the results, it was noted that incorporating MOEO nanoemulsion into the active films resulted in an elevation of their elasticity and resistance to water [13]. Another research revealed the development of active edible films using sodium caseinate, which contained a combination of zinc oxide nanoparticles (ZnONPs) and microcapsules of MOEO. The properties of the films were studied, and it was observed that they exhibited strong antioxidant activity [14].

To date, there has been no investigation into the impact of MOEO on the physiochemical characteristics of composite hydrogel-based films composed of pectin and collagen. Present study aims to investigate the effect of MOEO on the structural, mechanical, thermal, chemical, optical and barrier properties of hydrogel films based on pectin/collagen. In addition to investigating the physicochemical changes to determine the compatibility of the polymeric material with MOEO, the antioxidant activity was also evaluated as a potential food packaging material.
